Like a tortoise in a field of hares, American labor has plodded through the turbulence of the last quarter-century with less apparent movement than most other major institutions.

A generation that witnessed a dizzying parade of upheavals, fads and folk heroes also watched the aging of George Meany, the larger-than-life personification of an institution that made endurance its hallmark.

Even as the 85-year-old Meany prepares to step down next week after 57 years in the labor movement, including 24 years as the first and only president of the AFL-CIO, the emphasis is still on continuity.

Bowing to its ailing patriarch's wishes, the labor federation will vote Nov. 19 or 20, in the midst of its four-day biennial convention here, to replace Meany with his handpicked lieutenant, AFL-CIO Secretary-Treasurer Lane Kirkland.

The 57-year-old Kirkland is pledged to carry on the Meany legacy, and no one is expected to spoil the occasion by suggesting any other course.

But Kirkland also has asserted that organized labor is "on the threshold of another major surge forward," which some labor leaders say will demand substantial changes in the way unions serve their members and society.

Endurance is no longer enough, they are saying, and some cherished family heirlooms may be broken, including traditional approaches to organizing, labor-management relations and even work itself.

Kirkland's inheritance is a mixed bag of troubles and opportunities -- so much so that many unionists characterize the Meany-to-Kirkland succession as a major corssroads for the labor movement.

Unions are in an uphill race to overtake social and economic forces that, for the time being at least have left them choking in the dust. But they also are changing in composition and outlook, contradicting their own image of stodginess with ideas as venturesome as worker representation on corporate boards of directors and job-sharing by families.

Almost every major union has gotten a new president over the last decade, many of them technocrats who, like Kirkland, offer relative youth, a better education and a broader arsenal of skills as compensation for lacking their predecessor's roughhewn flair.

The AFL-CIO Executive Council is illustrative. Only eight of the 33 union president on the council were there a decade ago; after next week's convention their ranks will have shrunk to six. The council's members are almost exclusively middle-aged white males, but they can no longer be called old.

The rank-and-file composition of unions has changed even more dramatically: more younger and better educated workers, more women, more minorities. These workers, and others that unions would like to recruit, are making new demands that union leaders ignore at their peril.

Moreover, the economy's shift from a manufacturing to a service industry base is beginning to show up in the power balance at the top of Big Labor, in part because of the phenomenal growth of public employe unions over the past decade or so.

In just a couple of years, for instance, the United Steelworkers dropped from No. 1 in size in the AFL-CIO to No. 3 behind United Food and Commercial Workers and the American Federation of State, County and Municipal Employes.

Changes in the work force -- including the growth of service industries and the priorities of workers who view the Great Depression as ancient history -- have outstripped unions' ability to adapt.

Only one wage-earner in four belongs to a union, compared with one in three during the 1950s. When farm workers are counted, the figure drops to less than one in five, lower than that of most other industrialized nations. tUnions could claim only 20.2 million of a workforce of 102.5 million last year, according to the U.S. Bureau of Labor Statistics. Moreover, the trend has been steadily down, with no sign of a reversal.

Whole unions, or group of unions, are fighting to survive.

The construction industry, from which Meany earned his plumber's union card in 1910, is now more than half nonunion. The building trades union are shedding some of their jealously guarded exclusivity to keep from losing more ground.

The United Mine Workers Union which spearheaded the drive to unionize mass-production industries under the legendary John L. Lewis, now teeters on the brink of anarchy. Its members dig less than half the nation's coal, down sharply from just a few years ago.

Steel, electronics, garment and other unions watch foreign competition eat away at their job bases, while the nonunion American Sun Belt lures still other jobs away from the heavily unionized Midwest and Northeast. l

Many unions in import-threatened industries have closed ranks with corporations to campaign for ever-higher trade barriers, a symbiotic relationship that some believe erodes the traditional adversary system in American labor-management relations. The alternative -- making American products cheaper by reducing wages, benefits and other labor costs -- remains the ultimate in unspeakable heresy.

In terms of organizing, unions are struggling to appeal to computer programmers, bank tellers and nurses with techniques, slogans and services tailored largely for carpenters, machinists and miners.

They are whipsawed by shifting political moods. In public employment, where unions made their only major gains in recent years, organizers are bumping into budget-cutting restraints on civil service expansion.

Moreover, many employers are offering just enough wages and benefits to keep the unions at bay. At the same time, they promise freedom from union dues, work rules and seniority structures -- the security net of yesterday that many of today's young, female and minority workers see as an anachronistic obstacle.

Unions, which once won 80 percent of all their representation elections, are now losing more than they're winning: nearly 52 percent last year, according to the National Labor Relations Board. The number of decertification elections has grown fivefold since the 1950s, and unions lose roughly three out of four cases.

In the legislative arena, business has co-opted many of labor's lobbying and fund-raising techniques, blocking big union initiatives and, while not forcing labor to retreat on existing legislation, at least confining it to a restaging of old battles.

Unions have fought back largely by thundering at corporate American for replacing antilabor goons with slick consultants and lawyers -- by inviting "class warfare," in Kirkland's words. Unions have been slow to use the simplest of managerial and technological tools to mount new offensive of their own, but there are signs of more zeal to strike out in new directions.

Despite skepticism from some of their more traditionalist colleagues, such union leaders as Douglas A. Fraser of the United Auto Workers and Glenn E. Watts of the Communications Workers are moving in directions that once were considered beyond the pale.

Fraser has embarked on a European-styl "codetermination" venture by starved Chrysler Corp. for a seat on the company's board of directors. Although this strikes some as tantamount to buying a deck chair on the Titanic ("Wouldn't you know that they'd want to give us Chrysler," quipped Thomas N. Donahue, who is expected to succeed Kirkland as AFL-CIO secretary-treasurer), Fraser sees worker participation in corporate policymaking as an almost certain trend.

Watts is talking about new workplace concept, such as job-sharing among family members, flexible work assignments and bargaining for "quality of life rather than just wages and benefits."

While he doesn't go as far as Watts,Donahue believes unions must address such issues and tailor their services to "everything that happens in a worker's life." Fraser, going over farther than Watts, said he expects, as a new Chrysler board member, to submit a plan for the total democratization of the Chrsler work force" -- a corporation-wide extension of plant-level experiments within the General Motors Corp.

Meanwhile, the AFL-CIO, largely at Kirkland's initiative, borrowed from the European model of social contracts to enter into a "national accord" with the White House on economic policy. The pact already has enhanced labor's leverage on an administration thirsting for union support as it prepares for the 1980 elections.

Kirkland also has indicated he wants the independent Uaw andd International Brotherhood of Teamsters back in the AFL-CIO. They are expected to rejoin at some point, boosting the federation's membership from fewer than 14 million to more than 17 million and, in the case of the UAW, restoring one of labor's most progressive voices to AFL-CIO policymaking.

Interestingly it was Meany -- never the dinosaur that his critics portrayed -- who pointed recently to what may be the movement's toughest, challenge: organizing the public and private service sectors, including professional and other white-collar workers.

To the extent that unions are shaped by their tool-box and assembly-line origins,, such an expansion could have an extraordinary impact on labor's power base and its future.

Whether it can be done is an open question, although the cigar-chomping Meany was never one for pipe dreams. The relatively recent transformation of the National Education Association into a union in all but name, and a fairly militant one at that underscores the potential.

For all their troubles, unions are likely to be around for a long time, notwithstanding the National Association of Manufacturers' crusade for a "union-free' environment." Meany helped to insure that. Whether they thrive on wind up as vestigial relics of the Meany era depends on those who come after him.